Purification and characterization of a cholesterol-receptor protein present in rat liver cytosol will be continued. Studies of the number of specific binding sites and their affinities for cholesterol and other sterols will be made. The role of this receptor protein and of the chromatin-bound free and esterified cholesterol in the control of 3-hydroxy-3-methylglutaryl CoA reductase and of cholesterol biosynthesis in liver will be studied by use of perturbants in intact animals and in isolated hepatocytes.